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Acorn Computer

The Acorn Atom was the ancestor of the BBC computers series. It was sold in kit or ready-assembled versions.

The great advantage of the Atom compared to its competitors (TRS-80 & PET), was its high resolution capabilities (256 x 192) which were quite unusual in 1979 for the price.

The built-in BASIC was in some ways quite limited (it could only use integers for example) but an optional 4K ROM added the ability to use floating point numbers, trigonometric functions, to convert degrees/radians and to draw graphics in color. More add-ons were also available enabling autonumbering, a faster cassette interface (1200 bauds), and functions such as INKEY$, MID$, READ, DATA, FILL, etc... There was even a BBC BASIC board available.

A lot of applications were available on sideways ROMs that plugged into the "utility ROM socket" as Acorn called it, such as the "Atom Word Pack ROM" (word processing) or Atom-Calc (a 4K ROM spreadsheet).

A colour card was available, connected to the BUS connector, it provided 8 colors, 4 simultaneously at the 64 x 192 resolution or 2 at 128 x 192 for example. But it was known to overheat!

A lot of other peripherals were developed : - a 5.25" floppy disk drive (100K) which held the DOS in a 3K ROM but cost about twice as much as a new Atom!,
- a digital-tape recorder,
- a printer interface,
- a network card called EcoNet which enabled linking of up to 250 Atoms (210 K/Bauds transfer rate),
- RAM expansions,
- etc...


Mr Wobbler reports :
The overheating of the graphics card seemed due to the conversion from NTSC to PAL. THE VC chip could be just seen under the mountain of discrete components to convert the scan rate... Programming the atom was fun, allowing the mixing of in-line assembler code embedded in basic programs. This made the transition from high level to assembler programming easier. My father bought one and had 2 subsequent replacements supplied FOC by Acorn due to problems in the video circuitry (mostly the output frequency wandering).

Peter Passchier comments:
The speaker was not just a beeper. You have direct write access to the I/O port, and it could be made to beep at a particular pitch by 'toggling' the speaker at a particular frequency. I used to use a one-liner that I would type in manually at night to wake me up with a warble at a desired time in the morning!

Please consider donating your old computer / videogame system to or one of our partners from anywhere in the world (Europe, America, Asia, etc.).


Owner of two Acorn Atoms one of which is for sale on Ebay at this moment.

Thursday 12th April 2018
John Ferguson (UK)

I have found a Emulator of Acorn Atom, and printed out an manual to. So it''s gone be nice Basic programming.

I like to program Basic, but I''ll need manuals so I know how the Basic language work out. And what I can see so was Acorn Atom a good computer, the Basic is easy to understand.

Monday 14th April 2014
Mikael (Sweden)
Welcome To My Homepage

"A lot of applications were available on sideways ROMs that plugged into the "utility ROM socket" as Acorn called it"

The ROM sockets were continuous with the address space of the 6502, so did not need page switching. The Atom supported additional ROMs but they were not ''sideways'' ROMs.

Friday 1st July 2011
Atom User


MANUFACTURER  Acorn Computer
TYPE  Home Computer
ORIGIN  United Kingdom
YEAR  1980
BUILT IN LANGUAGE  Basic, machine-code
KEYBOARD  QWERTY, full-stroke keyboard, 60 keys
CPU  6502
SPEED  1 mHz
CO-PROCESSOR  6847 Video Display Generator, PIA 8255 (keyboard & tape)
RAM  2 KB (up to 12 KB, or 32 KB using external RAM expansion kit. )
ROM  8 KB (Atom BASIC and COS), up to 16 KB
TEXT MODES  32 x 24 / 16 x 12
GRAPHIC MODES  64 x 64 (4 colors), 64 x 96 (4 colors), 128 x 96 (monochrome), 64 x 192 (4 colors), 128 x 192 (2 colors), 256 x 192 (monochrome)
SOUND  Built-in beeper
SIZE / WEIGHT  15'' long x 9.5'' deep x 2.5'' high
I/O PORTS  Tape interface, UHF Modulated TV output, Acorn Bus Extension
POWER SUPPLY  External PSU - 8v 2A
PRICE  kit: £120
Built : £170
50£ (UK, 1983)
381 (France, 82)

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